Other Battery Life Factors
In the 1Ds Mk3 Manual, Canon advised that the battery life and number of shots decreases when:

The shutter button is pressed halfway for a prolonged period.

Autofocus is frequently activated without taking a picture.

The LCD Monitor is used a lot.

IS (Image Stabilization) on the lens is activated.

Some lenses draw more power from the camera’s battery during operation due to their physical (heavy lens elements that need more power to move) and electronic (type and technology of the IS employed) properties.